1. Field of Invention
The present invention relates to a liquid crystal display, and more specifically, it relates to a transflective liquid crystal display which can achieve reflective mode display and the transmissive mode display in a switching manner, and an electronic apparatus incorporating the liquid crystal display.
2. Description of Related Art
Reflective liquid crystal displays that achieve display by making use of the external light cannot be viewed in a dark location. Thus, such a reflective liquid crystal display has been typically used as a transflective display having an auxiliary light source. Most reflective color liquid crystal displays which have quickly become popular in recent years are also used as transflective color liquid crystal displays as disclosed, for example, in the following published international application (International Application Number: WO99/40480).
A configuration of a conventional transflective liquid crystal display is described below with reference to FIG. 8. FIG. 8 shows a first polarizer 801, a first retardation film 802, a second retardation film 803, a liquid crystal cell 804, a third retardation film 805, a second polarizer 806, and a backlight 807. The liquid crystal cell 804 includes a first substrate 811 and a second substrate 812, a liquid crystal 813, a scanning electrode 814 disposed on an inner surface of the first substrate 811, and a transflector 815 which is also used as a signal electrode disposed on an inner surface of the second substrate 812. The backlight 807 includes a light guide plate 821 and a reflector 822, and a light source 823.
Next, the operating principle of a conventional transflective liquid crystal display is described below with reference to FIG. 9. FIG. 9 shows a first polarizer 901, a first retardation film 902, a second retardation film 903, a liquid crystal 904, a transflector 905, a third retardation film 906, a second polarizer 907, a light guide plate 908, and a reflector 909. FIG. 9 also shows an ON area 911 of the liquid crystal 904, and an OFF area 912 of the liquid crystal 904. In the ON area 911, the selective voltage is applied to the liquid crystal 904, and the tilt angle, i.e., the angle formed between the liquid crystal molecule and the substrate surface, is increased. On the other hand, in the OFF area 912, the non-selective voltage is applied to the liquid crystal 904, and the tilt angle is decreased.
Firstly, the reflective mode display is described below. An external light 921 is converted into a linearly polarized wave by the first polarizer 901, transmitted through the first retardation film 902, the second retardation film 903 and the liquid crystal 904, and then converted into the circularly polarized wave in the ON area 911, or the linearly polarized wave in the OFF area 912. Thereafter, the light is reflected by the transflector 905, transmitted through the liquid crystal 904, the second retardation film 903, and the first retardation film 902, and converted into the linearly polarized wave orthogonal to the incident polarized wave in the ON area 911, absorbed by the polarizer 901 to form a black display 931, or converted into the linearly polarized wave parallel to the incident polarized wave in the OFF area 912, and transmitted through the polarizer 901 to form a white display 932.
Next, the transmissive mode display is described below. The light emitted from a backlight light source 922 is diffused by frosting or the like (not shown in the figure) cut in the light guide plate 908 while repeating the total reflection in the light guide plate 908, and emitted to the liquid crystal cell side. This light is converted into the linearly polarized wave by the second polarizer 907, and further converted into the circularly polarized wave by the third retardation film 906. Black can be displayed in the ON area 911, and slightly dark white can be displayed in the OFF area 912 by setting this circularly polarized wave so that it is circularly polarized in the same rotational direction as the circularly polarized wave when the external light incident in the ON area 911 of the liquid crystal in the reflective mode display is reflected by the transflector 905, for example, a clockwise circularly polarized wave. On the other hand, the circularly polarized wave reflected downward by the transflector 905 becomes counterclockwise circularly polarized, returned to the linearly polarized wave by the third retardation film 906, and then, absorbed by the second polarizer 907.
However, such a conventional transflective color liquid crystal display has a problem in that the transmissivity is low. As described above, this is attributable to the fact that the light of the backlight reflected by the transflector 905 is absorbed by the second polarizer 907 due to the conversion of the polarized wave by the third retardation film 906. The transmissivity of the transflector 905 is only about 5 to 15%, and thus, 85 to 95% of the light is actually wasted.
Accordingly, it is an object of the present invention to provide a transflective liquid crystal display of high transmissivity by recycling the light reflected by the transflector to enhance the efficiency of utilization of the light by making use of a backlight having a diffusing polarizer.
A structure in accordance with the present invention to address the above problem is described below.
The liquid crystal display in accordance with the present invention includes a liquid crystal cell having a liquid crystal held between a pair of substrates, a transflector disposed inside the liquid crystal cell, a backlight disposed outside of the liquid crystal cell, and a retardation film disposed between the liquid crystal cell and the backlight. The backlight includes a light guide plate and a light source. A diffusing polarizer is disposed on one side of the light guide plate, and a reflector is disposed on the other side of the light guide plate. The diffusing polarizer is a polarizer having the function of diffusing a predetermined component of the linearly polarized wave, and allowing the other component of the polarized wave to be transmitted. The retardation film has the function of converting the linearly polarized wave incident therein into the substantially circularly polarized wave, and preferably includes at least one xc2xc wavelength plate. The diffusing polarizer is preferably adhered to the light guide plate. In the above configuration, the linearly polarized wave is removed from the light guide plate by the diffusing polarizer, and converted into the circularly polarized wave by the retardation film and incident in the transflector. The light reflected by the transflector is also reflected by the reflector of the backlight, and recycled. Since no member that absorbs the light is present therebetween, most of the light of the backlight is transmitted through the transflector, which achieves a transmissive display that is brighter than a conventional transmissive display.
The liquid crystal display in accordance with the present invention further includes a retardation film that is disposed between the light guide plate of the backlight and the reflector. This retardation film also has the function of converting the linearly polarized wave incident therein into a substantially circularly polarized wave, and preferably includes at least one xc2xc wavelength plate. In particular, in the above liquid crystal display, the reflector of the backlight preferably has a reflecting surface that is close to a mirror surface, and disturbs no polarized wave. In the above configuration, the light reflected by the transflector is returned to the same polarized state, and recycled, and thus a bright transmissive display with high contrast can be obtained.
An electronic apparatus in accordance with the present invention includes the liquid crystal display according to any one of the above aspects of the present invention discussed above. This configuration provides an advantage of achieving a portable electronic apparatus having a long battery life and having a display that is easy to view.